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<p>The silico-ferrite phases of calcium and aluminum (SFCA) serve as the primary bonding agents in iron ore sintering, playing a crucial role in determining its mechanical strength and reduction characteristics. Among these phases, the SFCA-I polymorph demonstrates enhanced thermochemical stability and superior metallurgical properties. Nevertheless, the increasing concentrations of alumina and silica in lower-grade iron ores have substantially modified the phase equilibria within the CaO–Fe<sub>2</sub>O<sub>3</sub>–Al<sub>2</sub>O<sub>3</sub>–SiO<sub>2</sub> system. This study systematically investigates the effect of the Al<sub>2</sub>O<sub>3</sub>/SiO<sub>2</sub> mass ratio on the structural stability, lattice parameter evolution, and reduction behavior of SFCA-I. High-purity SFCA-I specimens with precisely controlled aluminum-to-silicon ratios were synthesized through high-temperature equilibrium quenching. Subsequent phase identification and characterization were performed using X-ray diffraction combined with Rietveld refinement, optical microscopy, and electron probe microanalysis. Results indicate that increasing the Al/Si ratio enhances the stability of SFCA-I, which is accompanied by a contraction in lattice dimensions and a decrease in porosity. Thermodynamic and kinetic analyses reveal that the transition from SFCA to SFCA-I occurs at an Al/Si ratio near unity, coinciding with the minimum melting temperature and the emergence of a single-phase SFCA-I region. Isothermal reduction experiments under CO–N<sub>2</sub> atmospheres show that higher Al/Si ratios reduce the apparent activation energy from 26.1 to approximately 12.3 kJ/mol, suggesting an accelerated reduction process, although the overall reducibility remains unaffected. These findings elucidate the compositional limits and mechanistic pathways governing the SFCA to SFCA-I transformation and reduction, thereby providing a quantitative framework for optimizing sintering processes involving high-alumina iron ores.</p>

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Effect of Al2O3/SiO2 Ratio on Phase Stability, Crystal Evolution, and Reduction Mechanism of SFCA-I in the CaO–Fe2O3–Al2O3–SiO2 System

  • 期刊论文

  • 发表日期：

    2026年3月13日

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  • Rui Wang,
  • Yongda Li,
  • Jian Xu,
  • Junjie Zeng,
  • Yuxiao Xue,
  • Mingrui Yang,
  • Yong Cheng,
  • Xuewei Lv

摘要

The silico-ferrite phases of calcium and aluminum (SFCA) serve as the primary bonding agents in iron ore sintering, playing a crucial role in determining its mechanical strength and reduction characteristics. Among these phases, the SFCA-I polymorph demonstrates enhanced thermochemical stability and superior metallurgical properties. Nevertheless, the increasing concentrations of alumina and silica in lower-grade iron ores have substantially modified the phase equilibria within the CaO–Fe2O3–Al2O3–SiO2 system. This study systematically investigates the effect of the Al2O3/SiO2 mass ratio on the structural stability, lattice parameter evolution, and reduction behavior of SFCA-I. High-purity SFCA-I specimens with precisely controlled aluminum-to-silicon ratios were synthesized through high-temperature equilibrium quenching. Subsequent phase identification and characterization were performed using X-ray diffraction combined with Rietveld refinement, optical microscopy, and electron probe microanalysis. Results indicate that increasing the Al/Si ratio enhances the stability of SFCA-I, which is accompanied by a contraction in lattice dimensions and a decrease in porosity. Thermodynamic and kinetic analyses reveal that the transition from SFCA to SFCA-I occurs at an Al/Si ratio near unity, coinciding with the minimum melting temperature and the emergence of a single-phase SFCA-I region. Isothermal reduction experiments under CO–N2 atmospheres show that higher Al/Si ratios reduce the apparent activation energy from 26.1 to approximately 12.3 kJ/mol, suggesting an accelerated reduction process, although the overall reducibility remains unaffected. These findings elucidate the compositional limits and mechanistic pathways governing the SFCA to SFCA-I transformation and reduction, thereby providing a quantitative framework for optimizing sintering processes involving high-alumina iron ores.